Gondola rail cars are characterized by design simplicity and efficiency in construction and operation. They feature a car body defining a generally rectangular box for holding cargo with side walls, end walls, and a bottom. The car body is supported on a frame which in turn is supported on pair of wheel trucks with wheels that ride on railroad rails. The cargo can be loaded and unloaded from an open top of the car body. Gondola cars are sometimes designed for rotary dump, where the entire car is held onto a rotary dump mechanism which turns the car about an axis parallel to the car's longitudinal axis, until reaching an almost inverted position, to empty the cargo.
Many thousands of gondola rail cars are in operation on railroads around the world, transporting bulk commodities such as coal, ore, aggregates, etc. Over time, design modifications and improvements have resulted in rail cars with increased efficiency and durability. Improvements which are modest when viewed in the context of an individual rail car, can nevertheless have a large overall financial and environmental impact because of the wide spread and intensive use of these rail cars.
Many years ago gondola rail cars were introduced with a unique bottom floor structure that helped increase the car's capacity and lower its center of gravity. Instead of a flat bottom floor mounted on top of a center sill, two longitudinal arcuate tubs were attached to and suspended between the center sill and side walls. An example of this design can be seen in U.S. Pat. No. 4,361,097, issued on Nov. 30, 1982 (hereinafter the '097 patent). Coal gondola cars using this design have been built and sold by FreightCar America and its predecessor companies under the BethGon® brand name. This patent application proposes modifications and improvements to the double longitudinal tub floor design and similar designs to continue to enhance efficiency, reliability, and durability.